The present trend in image storage is to use removable digital image storage devices that are generally useful as mass storage devices for digital computers. Such storage devices are not specifically adapted to the storage of image data and, indeed, may be used for storage of any kind of electronic data, including database information, word processor documents, software programs, etc. An example is the PC Memory Card adapted to the PCMCIA PC Card Standard--Release 2.0, published by the Personal Computer Memory Card International Association, Sunnyvale, Calif., September 1991. If such a memory card is used with an electronic camera, image data would be configured by the electronic camera to match the card interface standard, and then loaded into the card by a hardware interface that supports the card.
A variation on this memory concept is shown in U.S. Pat. No. 5,018,017, wherein image-specific information (e.g., exposure value, shutter speed) and camera-specific information (e.g., imaging system, compression mode in use) is loaded into a directory on the memory card. Patent application Ser. No. 868,163, "Memory Card with Programmable Interleaving" filed Apr. 14, 1992 by common assignee with the present application, goes beyond the above proposal by having a control circuit on the card for storing an interleave factor input from a host system for specifying the manner in which data is distributed among plural memory devices on the card. By varying the interleave factor, the host system can relate the data transfer rate to the particular application--i.e., if the host system is a personal computer the interleave factor can be small (or not used) as slow transfer rates are acceptable, but if the host system is a high resolution camera the interleave factor can be increased to provide real time transfer rates. A further image-specific example is shown in U.S. Pat. No. 4,887,161, wherein a memory card has a display and a processor for fetching stored images and putting them up on the display. (The processor also responds to a cancel input from the camera to erase unwanted images.)
Given the aforementioned trend toward PCMCIA-style memory cards, and despite some proposals for image-specific capabilities in digital storage devices, it remains the responsibility of the electronic camera to configure and manipulate the image data into a form suitable for storage. Because an image is described by a large amount of binary data, sometimes megabytes of data, it is a particular responsibility of the camera to compress and otherwise transform the data for storage. For instance, this may involve manipulation of color-spaces and image detail. As a result, the data in the digital storage device is only intelligible to a camera (or processor) of the type that originally configured and manipulated the data. What is needed is a storage technique that retains the advantages of present techniques, but presents a digital storage device as a generic device to a variety of camera and processor types.